The present invention relates to a hybrid yarn for composite materials with thermoplastic matrices, composed of thermoplastic fibers, as well as the method for obtaining same.
In current processes used to manufacture these types of composite materials, reinforcing fibers (carbon, aramide, or glass) in multifilament form are woven alternately with multifilaments of thermoplastic matrix fibers.
These thermoplastic matrix fibers belong to the classical families:
polyether ether ketone (PEEK), PA1 phenylene polysulfide (PPS), PA1 polyether imide (PEI), PA1 polyether sulfone (PES), PA1 polyamide. PA1 poor wettability, PA1 a large open-space ratio, PA1 delamination of the reinforcing fibers. PA1 cost of making the yarn, PA1 difficulties in weaving or braiding, PA1 difficulties in weaving or braiding, PA1 impossibility of making intricate fibrous parts since the network of continuous reinforcing fibers is nondeformable. PA1 very good wettability of the reinforcing fibers, PA1 very low open-space ratio, PA1 drapability of the textile surfaces allowing molding of developable or nondevelopable surfaces, PA1 highly isotropic material in the direction of the reinforcing fibers, PA1 excellent resistance to delamination. In fact, the material looks like a monolithic solid which has "forgotten" its original stratified structure.
This manufacturing technique has numerous drawbacks, including:
Another technique consists of commingling the multifilament of reinforcing fibers with the multifilament of thermoplastic fibers by a method known as "Commingled."
There are also other methods, which consist of filling the reinforcing fibers with a powdered thermoplastic matrix, the outside of which has a molten sheath containing the powder. There are also solvent impregnation processes, which have implementation problems, particularly in terms of worker safety and environmental impact. Inclusion of residual solvents in the composite is also prejudicial to good flame resistance.
These techniques all have substantial drawbacks in several areas:
Applicant's French Patent 2,634,790 teaches making a hybrid yarn for composite materials with a thermoplastic matrix by intimate mingling of reinforcing fibers and thermoplastic matrix fibers which have previously and independently undergone a cracking operation with slow, gradual stretching of the multifilaments.
The final strip obtained is then subjected to the classical spinning operations for long fibers: passage through a roving frame, spinning, winding, joining, and twisting.
The spun yarns thus obtained are able to be transformed by weaving, knitting, or braiding, to obtain composite materials having numerous advantages over materials of the same type obtained by methods of the prior art.
These advantages are the following:
The composite obtained may also be easily hot stamped.
DE-A-2,407,357 describes a yarn intended for garment fabrics obtained from a bundle of plant or animal fibers (cotton, wool) intimately mingled with polyester or polyamide. The wrapping technique of spinning is used in order to substantially improve the rate of production. This yarn has a wrapping filament which is of the same nature as the synthetic fiber in the mixture for dyeing affinity purposes. This wrapping filament, which is an integral part of the yarn and remains present in the final garment, also confers dimensional stability to the garment and reduces wrinkling of the fabric.